Photographic silver halide emulsions stabilized with pyrylium compounds



United States Patent 3,148,067 PHOTOGRAPHS SELVER HALEDE EMULSIONS TABILIZED WITH PYRYLIUM COWOUNBS George A. Reynolds, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of: New Jersey No Drawing. Filed June 22, 1962, Ser. No. 2M5?!) 10 Claims. (Cl. 96-109) This invention relates to photographic silver halide emulsions stabilized with certain heterocyclic compounds and to methods of preparing such emulsions.

It is well known that photographic emulsions on storage tend to lose sensitivity and to become spontaneously developable without exposure to light. There is normally a detectable amount of the silver salt reduced during development in the areas where no exposure was given; this is commonly called fog and sometimes called chemical fog where it is necessary to distinguish between it and the effects of accidental exposure to radiation; in this invention, we are not concerned with the latter.

Fog depends both on the emulsion and the conditions of development; for a given emulsion it increases with the degree of development. With constant development conditions, it tends to increase with time, temperature and relative humidity of storage conditions; it is common practice to make accelerated tests of the stability of photographic emulsions by storage at increased temperature or humidity, or both. It is, of course, desirable to have emulsions as stable as possible under the conditions of high temperature and humidity which may occur in tropical climates for example. Fog usually appears over the Whole area of the sensitive coating, but when severe, it frequently is non-uniform. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulfur compounds, hydrogen peroxide vapor, and strongly reducing materials. While antifoggants and stabilizers may protect, to some extent, against such effects, it is normally understood that an antifoggant protects against spontaneous growth of fog during prolonged storage or storage at high temperatures and humidities, or during development to maximum contrast and speed, or both.

It is, therefore, an object of my invention to provide a method of stabilizing photographic silver halide emulsions. A further object is to maintain the sensitivity and fog of such silver halide emulsions at, or close to, initial optimum values under keeping conditions of high temperatures and humidity. Other objects Will become apparent from a consideration of the following description and examples.

According to my invention, photographic silver halide emulsions can be stabilized against the formation of spontaneous fog by incorporating in the emulsions certain pyrylium salts. Such pyrylium salts which can be usefully employed in my invention include those represented by the following general formula:

wherein R R and R each represents an aliphatic radical, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tertiarybutyl, n-hexyl, n-octyl, isooctyl, n-nonyl, decyl, etc. (e.g., alkyl containing from 1 to 10 carbon atoms), alkoxyl, such as methoxyl, ethoxyl, propoxyl, butoxyl, pentoxyl, etc. (e.g., alkoxyl containing from 1 to 5 carbon atoms), hydroxyl, etc., or an aryl radical, such as phenyl, 0-, m-, and p-tolyl, 0-, m-, and p-hydroxyphenyl,

alkoxyphenyl (e.g., p-methoxyphenyl), etc., provided at least 2 of said R radicals are alkyl, and X represents an acid anion, such as a Water-solubilizing type, e.g., chloride, bromide, perchlorate, p-toluenesulfonate, methosulfate, etc.

The pyrylium compounds represented by the above general formula are quite unique in their stabilizing or antifoggant properties, since it has been found that closely related compounds do not have such useful properties. For example, compounds, wherein 2 or 3 of the R radicals are aryl, are very strong desensitizers. Moreover, related compounds which contain a sulfur atom in the position occupied by the oxygen atom in the above structure do not have the useful antifoggant or stabilizing properties demonstrated by the useful pyrylium compounds of the present invention.

The compounds of Formula I above can be prepared according to a number of general methods, including the following illustrative ones:

( a) OH Alk- Alk l A1k Alk C10 Alk o Alk Alb-L6 Alk C104- Other anionic derivatives of these compounds can be prepared, for example, by merely treating the Grignard intermediate of Procedure B with an acid (anion of acid becomes X in formula). Procedure C can be used to prepare alkyl sulfate salts, which can be converted to less soluble forms easily. Procedure D yields AlClp, BF; and SO;- salts. Other methods of preparing these compounds are illustrated in the copending application of I. A. Van Allan, C. C. Natale and F. J. Rauner, Serial No. 146,743, filed October 23, 1961. Typical pyrylium salts which can be used in my invention include the following: 2,6-dimethyl-4-methoxypyrylium perchlorate on. arn, 0104 =3 2,6-dimethyl-4-ethoxypyrylium perchlorate O C 2H5 on fij-on 0107 2.6-dirnethyl-4 hydroxypyrylium perchlorate om-[j-on, 01046 2,4,6-trimethylpyrylium perchlorate (mag-on, 0101 2,6-dimethyl-#phenylpyrylium perchlorate 2,6-diisopropyl-4-methylpyryliun1 perchlorate (3H (CHshCH omen, c104 2,6-dimethyl-4-amylpyrylium perchlorate OH LO CH 010.,

4-acetoxy-2,6-dimethylpyrylium fluoroborate (8) OCOCH CH CH 4-butoxy-2,6-dimethylpyryliurn perchlorate O CAHB on 1. OH:, 010,

room temperature, g. of 20 percent aqueous perchloric acid added, and after chilling, the long white needles were collected, M.P. 215-6 C. (yield=6 g.). The reported melting point is 126-7 C.; J. Chem. Soc. (1946), 117.

2,6-dimethyl-4 hydroxypyrylium perchlorate: A solution of 2 g. 2,6-dimethyl-4-pyrone in 100 ml. of ether was saturated with hydrogen chloride. The 2,6-dirnethyl-4- hydroxypyrylium chloride that separated was collected on a Biichaer funnel and washed with ether. To a concentrated solution of the pyrylium chloride in alcohol was added 2 ml. of percent perchloric acid and the mixture chilled. The product was collected and Washed with ether (yield-:22 g.).

2,4,6-trimethylpyryliun1 perchlorate: (1927).

2,6-dimethyl-4-phenylpyrylium perchlorate: Ann, 432, 297 (1923).

Ben, 60, 722

2,6-diisopropyl-4-methylpyrylium perchlorate: Ann, 625, 74 (1959).

2,6-dimethyl-4-amylpyrylium perchlorate: A solution of amylmagnesium bromide (prepared from 15 g. of 1- bromopentane, 2.4 g. of magnesium and ml. of ether) was added slowly with cooling and stirring to 14 g. of 2,6- dimethyl-4-pyrone in 250 ml. of dry tetrahydrofuran. The mixture was stirred for one hour and then acidified with aqueous perchloric acid. The reaction mixture was concentrated at room temperature to half volume and then chilled to yield 4 g. of product as long white needles, M.P. C.

The stabilizing compounds of my invention are particularly useful in photographic developing-out emulsions, including many of the conventionally employed silver halide emulsions, such as silver chloride, silver bromide, silver brorniodide, silver chlorobromide, silver chlorobromiodide, etc.

The emulsions can be chemically sensitized by any of the accepted procedures. The emulsions can be digested with naturally active gelatin, or sulfur compounds can be added such as those described in Sheppard US. Patent 1,574,944, issued March 2, 1926, Sheppard et al. US. Patent 1,623,499, issued April 5, 1927, and Sheppard et al. US. Patent 2,410,689, issued November 5, 1946.

The emulsions can also be treated with salts of the noble metals such as ruthenium, rhodium, palladium, iridium, and platinum. Representative compounds are ammonium chloropalladate, potassium chloroplat-inate, and sodium chloropalladite, which are used for sensitizing in amounts below that which produces any substantial fog inhibition, as described in Smith and Trivelli US. Fatent 2,448,060, issued August 31, 1948, and an antifoggants in higher amounts, as described, in Trivelli and Smith U.S. Patents 2,566,245, issued August 28, 1951, and 2,566,263, issued August 28, 1951.

The emulsions can also be chemically sensitized with gold salts as described in Waller et al. U.S. Patent 2,399,- 083, issued April 23, 1946, and Damschroder et al. US. Patent 2,642,361, issued June 16, 1953. Suitable compounds are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and 2- aurosulfobenzothiazole methochloride.

The emulsions can also be chemically sensitized with reducing agents such as stannous salts (Carroll US. Patent 2,487,850, issued November 15, 1949), polyamines, such as diethylene triamiue (Lowe and I ones US. Patent 2,518,698, issued August 15, 1950), polyamines, such as spermine (Lowe and Allen US. Patent 2,521,925, issued September 12, 1950), or bis(fi-aminoethyl) sulfide and its Water-soluble salts (Lowe and Jones US. Patent 2,521,: 926, issued September 12, 1950).

The emulsions can also be optically sensitized with cyanine and merocyanine dyes, such as those described in Brooker US. Patents 1,846,301, issued February 23, 1932; 1,846,302, issued February 23, 1932; and 1,942,854, issued January 9, 1934; White US. Patent 1,990,507, issued February 12, 19 35; Brooker and White US. Patents 2,112,-

140, issued March 22, 1938; 2,165,338, issued July 11, 1939; 2,493,747, issued January 10, 1950, and 2,739,964, issued March 27, 1956; Brooker and Keyes US. Patent 2,493,748, issued January 10, 1950; Sprague U.S. Patents the silver halide emulsion in order to obtain optimum results. The quantity of stabilizing compound can be varied, depending somewhat upon the chemical activity of the stabilizer, the concentration of silver halide in the emulsion,

2,503,776, issued April 11, 1950, and 2,519,001, issued 5 coating thickness of the emulsion, and the like. In gen- August 15, 1950; H ltin and Brooker US P t 2; eral, I have found that optimum results can be obtamed 666,761, issued January 19, 1954; Heseltine US. Patent at concentrations of from about 0.25 to about 6.0 gra 2,734,900, issued February 14, 1956; Van Laro US. Patp mol of i e hahde m the emulslonent 2,739,149, issued March 20, 1956; and Kodak Limited The following examp es Wi l serve to illustrate h British Patent 450,958, accepted July 15, 1936. 10 fill ,efiects of the P Y F COmPPImdS f inventlon The emulsions may also contain speed increasing comfl P grap ic sllv r halide emuls ons. pounds of the quaternary ammonium type of Carroll U.S. A hlgh-speed gelatmmbromlodlde 911111151011 was dlvlded P t 2,271,623, issued February 3, 1942; Carroll and Into several batches and a portion of each batch removed Allen US. Patent 2,288,226, issued June 30, 1942; for p p of serving as a control To each of the and Carroll and Spence U.S. Patent 2,334,864, issued 1 maining portions Was added a small amount of antifog- November 23, 1943; or the polyethylene glycol type of gant and the batches, together with the control emulsions, Carroll and Beach U.S. Patent 2,708,162, issued May 0, coated on a conventlonal photographic support, such as 1955; or the quaternary ammonium salts and polyethylene cellulose acetate film. The coatings were tnen dried and glycols of Piper Patent 2,886,437, issued May 2 exposed for sec. in an Eastman Type Ib sensltometer. 1959; as well as the thiopolymers of Graham and Sagal The film Samples were then developed In a conventlonal US application Serial 779,339, filed December 2 black-and-Wlnte developer, such as one having the follow- 1958, and the Dann and Chechak US. application Serial composltloni No. 779,874, filed December 12, 1958. Grams In the preparation of the silver halide dlSPCISlOIlS em- N'methyl'p'amlnoplilenol Sulfate l d f preparing ilver halide emulsions, there may be sodfum Sulfite (desiccated) 100 employed as the dispersing agent for the silver halide in Sodium mfitaborate it ation, gelatin or some other colloidal mat rial Sodium} thlocyanflte h as fl id l albumin, a cellulose derivative or a syn- Potassmm bromle thetic resin, for instance, a polyvinyl compound. Some Water to make 1 men C l i s Which m y be used are P YY Y a The developed emulsions were then fixed, washed and hydmlyzed P Y Y acetate as descrlbed 1n Lowe dried. The relative speed, gamma and fog for each of Patent Issued June 16, 1942; a far hydrolyzed the coatings Were then measured. A second set of coatings cellulose ester such as cellulose acetate hydrolyzed to an was prepared in exactly the am manner and th s oatacetyl content of 19-26% as dGSCIIbBd 1n US. Patent i were held f one Week at 120 R and 5 0 percent 2,327,308 of Lowe and Plafk, Issued August a relative humidity before use. These coatings were likewater-soluble ethanolannne cellulose acetate as descnbed wise exposed, fixed, Washed and dried as described abov in Yutzy Pate t 2 Issued 111.116 a The relative speed, gamma and fog for the incubated coatp y y g or an lmldlzed polyacrylamlde as desgrlbed ings were then measured, and the data obtained, together 111 LOWe, Mlllsk and F Y Patfifllt 2,541,474, Issued with the fresh tests, are given in the following table. In February 13, 195 Zeln as descflbed Lowe Patent 40 the table, the compound numbers correspond to those for- 2,5 63,791, lssued August 7, 1951; a v1nyl alcohol polymer l d above Table A Fresh tests l-week incubation at Gone. in 120 F. and RH Coating Compound grams/ number No. Ag mole Rel. Gamma Fog Rel. Gamma Fog speed speed C0ntr01 100 0.90 0.10 0.73 0. 28 1 3.0 110 1.08 0.08 91 0.88 0.14 Control--- 100 1.10 0.11 83 0.92 0.23 5 0.75 87 1.17 0.11 0.93 0.18 5 3.0 58 1.12 0.08 73 1.00 0.11 C0ntrol 100 1.13 0.10 74 0.95 0.24 4 1.5 94 1.15 0.11 1.15 0.18 4..-- 3.0 74 1.12 0.12 83 0.97 0.14 7...- 3.0 100 1.15 0.11 85 0.97 0. 20 Cont 100 1. 22 0.12 02 0.83 0.24 0 75 1.18 0.12 32 0.88 0.20 Control-.. 1.18 0.12 91 0.92 0. 33 2 3.0 1.18 0.11 87 1.02 0.29

containing urethane carboxylic acid groups of the type described in Unruh and Smith US. Patent 2,768,154, issued October 23, 6; or containing cyano-acetyl groups such as the vinyl alcohol-vinyl cyanoacetate copolymer as described in Unruh, Smith and Priest US. Patent 2,808,- 331, issued October 1, 1957; or a polymeric material which results from polymerizing a protein or a saturated acylated protein with a monomer having a vinyl group as described in US. Patent 2,852,382, of Illingsworth, Dann and Gates, issued September 16, 1958.

The pyrylium salts of my invention can be added to the emulsions during the preparation thereof, or during the final digestion or immediately prior to coating. It is essential that the stabilizing agent be thoroughly mixed with The stabilizing compounds of my invention can be used in a wide variety of silver halide emulsions, including those intended for black-and-White photography, color photography (including emulsions containing color couplers, or those intended for processing in a color developer containing the coupler), X-ray emulsions, emulsions designed for use in diffusion transfer photography, and the like.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be eifected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What I claim as my invention and desire secured by Letters Patent of the United States is:

1. A photographic silver halide emulsion containing as an antifoggant a stabilizing amount of the compound selected form those represented by the following general formula:

wherein R R and R each represents a radical selected from the class consisting of alkyl containing from 1 to 10 carbon atoms, alkoxyl containing from 1 to 5 carbon atoms, hydoxyl and aryl, provided at least 2 of said radicals represent alkyl containing from 1 to carbon atoms, and X represents an anion.

2. A photograuhic silver halide emulsion containing a stabilizing amount of pyrylium salt selected from those represented by the following general formula:

wherein R R and R each represents alkyl containing from 1 to 10 carbon atoms and X represents an anion. 3. A photographic silver halide emulsion containing a stabilizing amount of a pyrylium salt selected from those represented by the following general formula:

wherein R and R each represents alkyl containing from 1 to 10 carbon atoms, R represents alkoxyl containing from 1 to 5 carbon atoms and X represents an anion.

4. A photographic silver halide emulsion containing as an antifoggant a stabilizing amount of a compound selected from those represented by the following general formula:

wherein R and R each represents alkyl containing from 1 to 10 carbon atoms, R represents aryl and X represents an anion.

5. A photographic silver halide emulsion containing a stabilizing amount of a pyrylium salt selected from those represented by the following general formula:

wherein R and R each represents alkyl containing from 1 to 10 carbon atoms, R represents hydroxyl and X represents an anion.

6. A photographic silver halide emulsion containing a stabilizing amount of the compound represented by the following formula:

om -on 01046 EB 7. A photographic silver halide emulsion containing as an antifoggant a stabilizing amount of the compound represented by the following formula:

8. A photographic silver halide emulsion containing a stabilizing amount of the compound represented by the following formula:

CH OHg 0104 9. A photographic silver halide emulsion containing a stabilizing amount of the compound represented by the following formula:

10. A photographic silver halide emulsion containing a stabilizing amount of the compound represented by the following formula: 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING AS AN ANTIFOGGANT A STABILIZING AMOUNT OF THE COMPOUND SELECTED FORM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 